Coating organic films with mixture of amorphous and crystalline dispersions of vinylidene chloride copolymers



United States Patent M 3,108,017 COATING ORGANIC FILMS WITH MIXTURE 0FAMORPHOUS AND CRYSTALLINE DISPERSIONS OF VINYLIDENE CHLORIDE COPOLYMERSGiinther Messwarb, Kelkheim, Taunus, and Kurt T. Schotte and WilhelmDummer, both of Wiesbaden, Germany, assignors to Farbwerke HoechstAktiengesellschaft vormals Meister Lucius & Briining, Frankfurt am Main,Germany, a corporation of Germany No Drawing. Filed Nov. 25, 1960, Ser.No. 71,460 Claims priority, application Germany Nov. 28, 1959 9 Claims.(Cl. 117138.8)

The present invention relates to an improved method for coating articlesof macromolecular organic substances with the use of an aqueousdispersion of a copolymer of vinylidene chloride.

Copolymers containing a predominant proportion of vinylidene chloridemeet in many respects with increasing interest as material for coatingpaper, films and sheets. Sheets treated with such copolymers are lesspermeable to steam and gas, exhibit improved aroma-preserving propertiesand possess an improved stability to solvents and chemicals.

The copolymers which are predominantly used for coating containvinylidene chloride in a proportion of 8095 It is known that articleswhich are coated with a dispersion containing a relatively highproportion of vinylidene chloride in the polymer (592% exhibitespecially favorable sliding properties. The blocking eifect, i.e.deficiencies produced by agglutination of wound up films, can readily beovercome by admixing the dispersion with wax.

The above dispersions involve, however, considerable disadvantages inthat the substantially amorphous structure of the polymer particles,which is first obtained by polymerization in an aqueous emulsion, issoon transformed, in most cases within some days or so, into the morestable crystalline state. Dispersions of substantially crystallinevinylidene chloride copolymers are, however, unsuitable for makingcoherent coatings. It is therefore rather difiicult to store suchdispersions and to use them at an appropriate time for coating.

If relatively soft dispersions are used, i.e. dispersions of a copolymercontaining vinylidene chloride in a proportion of less than 92% in thepolymer phase, it is possible to increase the lifetime of the amorphousstructure of the polymer particles to last for weeks or months. Coatingsproduced with such dispersions have, however, a stronger tendency toexhibit a blocking effect. The sliding properties of surfaces coatedwith such soft dispersions leave very much to be desired, and onlyrelatively little can be done to remove these disadvantages even byadmixing the dispersions with an ester wax, for example carnauba wax. Onthe other hand, coatings produced with such soft dispersions alsoexhibit some favorable proper-ties. The coatings exhibit favorable heatscaling properties and appear to be more flexible and elastic than thoseproduced with a harder dispersion of a vinylidene chloride copolymer.

The present invention which avoids all the aforesaid disadvantages isbased on the observation that coatings of good film properties can beproduced on articles of macromolecular organic materials by using anaqueous dispersion of a copolymer of vinylidene chloride. Moreparticularly, the coatings are produced using a dispersion mixturecontaining 50-99% by weight (calculated on the content of solid in themixture) of a dispersion of substantially amorphous copolymer particlesand 50 t0 1% by Weight (calculated on the content of solid in themixture) of a dispersion of substantially crystalline copolymerparticles.

3,108,017 Patented Oct. 22, 1963 Generally, the mixture is preparedimmediately before it is being used, but it may be stored, if desired.

The amorphous component in the above dispersion mixture isadvantageously a dispersion which contains vinylidene chloride in aproportion of 85-92% in the polymer. Dispersions of that type can beobtained, for example, by the process disclosed in U.S. patentapplication, Serial No. 17,446, filed February 23, 1960, by GiinterMesswarb et al., and now abandoned. These dispersions offer theadvantage that the polymer particles remain in their amorphousstructural state for a relatively long period of time so that they canbe used over a prolonged period.

The crystalline dispersion component in the above dis persion mixturemay be produced by any process imparting to the polymer the property ofbeing substantially converted into its crystalline state in thedispersion. Heterogeneous copolymerization, for example, produces thedesired eifect with the formation of chemically very heterogeneouscopolymers.

The process of this invention may be carried out using any dispersionwhich is based on a vinylidene chloride copolymer containing 85-95%vinylidene chloride but does not form a transparent and/ or coherentfilm. These dispersions, when admixed with a suificient quantity, forexample l3%, calculated on the dispersion, of an appropriate emulsifier,such as used in German Patent 821,615, have a longer lifetime thandispersions of analogous chemical structure which are usually employedand have the tendency to undergo crystallization. It would thereforeappear easy to those skilled in the art to select that dispersion whichis suitable for carrying out the process of this invention. It hasunexpectedly been found that a mixture of a dispersion containingsubstantially amorphous particles with a second dispersion whose polymerparticles themselves cannot form a transparent coherent film producescompletely transparent coatings having improved film properties,provided that the two dispersions are mixed with one another in anappropriate ratio. More especially, the dispersion mixture contains amaximum of A of solid material in the form of crystalline polymer.

The dispersion mixture generally contains solid material in a proportionof 10-50%, calculated on the weight of the dispersion mixture.Especially good results are obtained using a dispersion mixture whichcontains 20- 40% solid material.

The term vinylidene chloride copolymers as used herein is intended tomean polymers containing 70-95%, preferably 92% vinylidene chloride and305%, preferably 208%, of at least one monomer copolymerizable withvinylidene chloride. As copolymerizable monomers there may be mentionedmore especially: vinyl chloride, acrylonitrile, methacrylonitrile,acrylic acid esters, methacrylic acid esters, maleic acid esters,fumaric acid esters, itaconic acid esters, the alcohol constituents ofthese esters containing 16 carbon atoms and preferably not more than 4carbon atoms; there may also be used methylvinyl ketone, vinyl acetateand other vinyl esters, styrene, dichlorovinylidene fluoride, butadiene,chlorobutadiene, isoprene or vinylpyridine.

The articles which are coated according to this invention include hollowbodies, tubes or plates or films and sheets made from conventionalmacromolecular organic substances of natural or synthetic origin. Theremay be mentioned more especially: cellulose in native or regeneratedform, for example paper, and the chemical conversion products ofcellulose, such as cellulose esters, for example acetyl cellulose,nitrocellulose, cellulose acetatebutyrate, or cellulose ethers, forexample methyl cellulose or ethyl cellulose. There may also be usedthermoplasts, such as polyolefins, more especially polyethylene andpolypropylene, polyvinyl chloride, copolymers of vinyl chloride, forexample those with the aforesaid monomers, polyethylene terephthalate,mixtures of polyvinyl chloride and halogenated polyolefins, for examplechlorinated polyethylene, polyvinyl alcohol, alginic acid derivatives,gelatin, casein; or polyamides, for example those of hexarnethylenediamine and adipic acid or sebacic acid, polycaprolactam or polyvinylacetals.

The polymer dispersion may also contain a small proportion, i.e. about0.01 to 5%, advantageously 03-06%, calculated on the weight of thesolid, of a substance known as sliding agent or more especially anatural or synthetic ester wax. There may be mentioned more especially:carnauba wax, spermaceti wax, candelilla wax or palm wax, orhydrogenated castor oil, benzyl stearate, pentaprepared as described inExample 1 of British Patent 804,285.

(D) A mixture prepared from 2 parts of dispersion (A) and one part ofdispersion (C).

The following coating results were obtained:

Addition of carnauba wax in percent, calculated on solid TransparencySteam permeability, g./m. 24 h.

Period during which dispersion can be used Sliding properties Filmformation Blocking (A) without /2- (0) without (D) without good poor..good oor moderategood strong moderate" good 1 month D o. stable for 3weeks only.

1 month.

poor good 1. 6 good n0 erythritol-distearate,pentaerythritohtetrastearate or noctadecylstearate.

The articles are coated with the dispersion mixture used in thisinvention in known manner, for example, as described in British Patents663,645 and 744,669 or in German Patent 821,615 or in Modern Plastics,1958, pages 90 et seq. Aqueous dispersions are generally used butdispersions in another dispersing medium may also be used.

In order to improve the adhesiveness of the coatings produced, anintermediate layer of a fastening agent, such as a ureaformaldehyderesin or a reaction product of said resin with glycerol or glycol (U.S.Patent 2,728,688), polyalkylene imines (German Patent 752,810 andBritish Patent 766,827) or another suitable substance, may be applied tothe article.

The following example serves to illustrate the invention, but it is notintended to limit the invention thereto:

Example I A commercial film of regenerated cellulose which had beenpretreated by the process disclosed in British Patent 766,827, Example1, with glycerol and polyethylene imine, was coated as described in theexample of British Patent 744,669 on either side with about 5 g./m. each(calculated on the dry substance) of the following copolymer dispersionsat a rate of coating of m./min.

(A) An aqueous dispersion of 91.5% vinylidene chloride 6.8%methylmethacrylate 1.2% acrylonitrile 0.5% itaconic acid The dispersionwas prepared by the process described in the above US. patentapplication Serial No. 17,446 and contained 66.7% chlorine, calculatedon the solid substance.

(B) An aqueous dispersion of 93.0% vinylidene chloride 6.5%methylmethacrylate 0.5 itaconic acid The same coating results wereobtained on sheets of polyethylene, polyethylene terephthalate or amixture of vinyl chloride and chlorinated polyethylene.

We claim:

1. A process which comprises coating an article of a macromolecularorganic substance with a mixture of aqueous vinylidene chloridecopolymer dispersions, one dispersion containing substantially amorphouscopolymer particles in a proportion of 50 to 99% by weight, calculatedon the solids content of the total dispersion mixture, and the seconddispersion containing substantially crystalline copolymer particles in aproportion of 50 to 1% by weight, likewise calculated on the solidscontent of the total dispersion mixture.

2. The process of claim 1 wherein the macromolecular organic material isa film of regenerated cellulose.

3. The process of claim 1 wherein the macromolecular organic material isa film of paper.

4. The process of claim 1 wherein the macromolecular organic material isa film of polyethylene tereph-thalate.

5. The process of claim 1 wherein the macromolecular organic material isa film of polyethylene.

6. The process of claim 1 wherein the macromolecular organic material isa film prepared from a mixture of a polyvinylchloride and a chlorinatedpolyolefin.

7. The process of claim 1 wherein an ester wax emulsion is added to thepolymer dispersion as a sliding agent.

8. The process of claim 1 wherein the copolymer consists of -95%vinylidenchloride and 205% acrylonitrile.

9. The process of claim 1 wherein the copolymer consists of 8095%vinylidene chloride and 205% of a methacrylic acid ester.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS WHICH COMPRISES COATING AN ARTICLE OF A MACROMOLECULARORGANIC SUBSTANCE WITH A MIXTURE OF AQUEOUS VINYLIDENE CHLORIDECOPOLYMER DISPERSIONS, ONE DISPERSION CONTAINING SUBSTANTIALLY AMORPHOUSCOPOLYMER PARTICLES IN A PROPORTION OF 50 TO 99% BY WEIGHT, CALCULATEDON THE SOLIDS CONTENT OF THE TOTAL DISPERSION MIXTURE, AND THE SECONDDISPERSION CONTAINING SUBSTANTIALLY CRYSTALLINE COPOLYMER PARTICLES IN APROPORTION OF 50 TO 1% BY WEIGHT, LIKEWISE CALCULATED ON THE SOLIDSCONTENT OF THE TOTAL DISPERSION MIXTURE.